While I'm on the topic of the Data module, I'd like share my thoughts on some of the confusion surrounding use of the Data Node module included with the package. (see issues 976292 and 898562)
It's my opinion that the bulk of the functionality in the Data Node module has been intentionally "left undone." Instead, the module is giving us the tools to allow us to implement node relationships as needed, ourselves (think API). My thinking is that this was done to allow the maximum amount of flexibility in relating other data to nodes by minimizing assumptions about what the relationship should be. I have in no way validated this with any of the module maintainers, nor is it denoted in any documentation that I am aware of. What follows is my "average" use case for this module, and some thoughts on more advanced implementations.